1. Field of the Invention
The present invention relates to a cathode-ray tube apparatus provided with short-circuit loops for reducing leakage magnetic fields generated from the apparatus, especially those leakage magnetic fields from a deflection yoke.
2. Description of the Related Art
Recently, influences of leakage magnetic fields leaking from the deflection yoke of cathode-ray tube apparatuses to its surroundings upon a person have been put in question, and there has been an increasing demand for the development of an improved cathode-ray tube apparatus in which the leakage magnetic fields can be reduced.
As a measure to suppress leakage magnetic fields around the cathode-ray tube apparatuses, there is a conventionally known method in which a metal plate is used to cover the whole deflection yoke. In this case, however, the metal plate cannot be located in front of the screen, so that the effect of leakage magnetic field reduction is inadequate, and it is difficult to reduce leakage magnetic fluxes to a desired level. Inevitably, moreover, the apparatus is large-sized.
In order to solve these problems for the case where the metal plate is used to restrain the leakage magnetic fields, a method using auxiliary coils is disclosed in U.S. Pat. No. 4,709,220 and Published Unexamined Japanese Patent Application No. 62-64024, for example. The auxiliary coil is formed having substantially the same shape as that of a saddle-shaped horizontal deflection main coil which constitutes a part of the deflection yoke, and is arranged outside the main coil so as to hold a core therebetween. Leakage magnetic fluxes from the horizontal deflection main coils are reduced by feeding part of electric current flowing through the main coils to the auxiliary coils, thereby causing the auxiliary coils to generate magnetic fluxes.
According to this method in which part of the horizontal deflecting current is supplied to the auxiliary coils, however, the load of the auxiliary coils causes a loss to the horizontal deflection sensitivity of the deflection yoke. Further, terminals or the like must be provided for connecting the auxiliary coils to a horizontal deflection system, so that the construction of the apparatus is inevitably complicated. The auxiliary coils are connected electrically to the deflection system including the horizontal deflection main coils. In case of a conduction failure in the auxiliary coil circuit system, therefore, image display will be hindered. Thus, the reliability and safety of the cathode-ray tube apparatus are lowered.
As a measure to solve the problems of the method using the auxiliary coils of the current supply type, a method using short-circuit loops which are not connected electrically to the deflection system is described in Published Unexamined Japanese Utility Model Application No. 62-82555, for example. According to this method, although leakage magnetic fields in the vicinity of transitive portions of the main deflection coils can be reduced, leakage magnetic fields in front of the screen cannot.
Described in Published Unexamined Japanese Patent Application No. 3-16394, moreover, is a method in which leakage magnetic fields are reduced using short-circuit loops of an electrical conductor, which include no additional circuit or element. These short-circuit loops are arranged in an interlinked region between where a magnetic flux in the direction opposite to deflected main magnetic fluxes ranging from the front transitive portions of the main deflection coils to the screen. In this case, however, the short-circuit loops should be located in the region through which the magnetic flux passes opposite to the deflected main magnetic fluxes, and parts of the loops must be located close to the transitive portions of the main deflection coils. Thus, the location of the short-circuit loops can enjoy no freedom, so that their mounting efficiency is low, and image deterioration may be caused by a change of the landing position of an electron beam.